This invention relates to unplasticized or plasticized, stabilized compositions, especially thermoplastic compositions based on homo and copolymers of vinyl chloride and the like, and in particular to a new stabilizer system, especially a new costabilizer.
It is known that chlorine-containing polymers readily suffer degradation by the action of heat, for example during processing, leading to undesirable discolorations and impairment of mechanical properties. In order to avoid such degradation, stabilizers are thus added to the polymers prior to processing. For polyvinyl chloride and copolymers containing predominantly vinyl chloride, compounds employed as stabilizers are, in particular, organotin compounds, inorganic and organic lead salts, organic antimony compounds, or combinations of cadmium carboxylates and barium carboxylates. Frequently, costabilizers are added to these so-called primary stabilizers to improve the effectiveness of the latter. The mechanism of primary stabilizers and costabilizers has been described in the literature, for example in the publication by L. I. Nass, "Heat Stabilizers" in Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 12: 225, 3rd ed., publishers John Wiley and Sons, 1980.
The disclosed primary stabilizers, though exhibiting adequate efficiency, include lead, antimony and cadmium compounds which, on account of their toxicity, cannot be utilized in all areas, particularly in packaging materials for foodstuffs or in the medical field. Organotin compounds, many of which are toxicologically harmless, are unsuitable for wide-range application since they are too expensive, i.e., they are difficult to obtain and/or are producible only by an expensive process.
There is thus a need for stabilizer systems comprised of components which are physiologically acceptable and which are inexpensive and/or readily accessible. One possibility is offered by the use of fatty acid salts of calcium and zinc as primary stabilizers, optionally supplemented by costabilizers, such as epoxy compounds, organic phosphites, polyhydric alcohols, or 1,3-diketones. However, the disadvantage of these stabilizing systems resides in a lack of long-term stability and/or in the unsatisfactory initial coloring of the polymer composition. Costabilizers for stabilizer systems based on zinc, which markedly improve the initial and long-term effects of primary stabilizers, are mercapto compounds, such as mercapto succinic acid diesters (EP-B No. 0 111 896 of Dec. 15, 1983/June 27, 1984) and thioglycolic acid esters (EP-B No. 0 022 047 of June 24, 1980). However, these compounds exhibit the very disadvantageous property of having an extraordinary unpleasant odor occurring during incorporation into the polymer and during storage.